Method for manufacturing low noise pneumatic tire

ABSTRACT

A pneumatic tire having a noise damper, a method for manufacturing the same, and a method for fixing the damper to the tire are disclosed. The inner surface of the tread portion of the vulcanized tire is buffed, and the noise damper is fixed to the buffed inner surface, using a double-sided adhesive tape which has specific characteristics such as adhesive force, tensile strength, thickness, cold-resistant property, heat-resistant property and water-resistant property.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 11/584,600filed on Oct. 23, 2006, now U.S. Pat. No. 7,669,628, issue Mar. 2, 2010,the entire contents of which are hereby incorporated by reference andfor which priority is claimed under 35 U.S.C. §120. This nonprovisionalapplication also claims priority under 35 U.S.C. §119(a) on PatentApplication Nos. 2005-308882 and 2005-352437 filed in Japan on Oct. 24,2005 and Dec. 6, 2005, respectively, the entirety of which is hereinincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a pneumatictire having a noise damper, more particularly to a method for fixing anoise damper to the inner surface of a vulcanized tire.

2. Background of the Invention

In order to reduce a tire noise generated during running, a noise dampermade of a sponge material and disposed in a tire cavity has beenproposed, for example, as disclosed in Japanese patent applicationpublication No. 2003-063208.

Such a noise damper prevents or interrupts resonances of the tirecavity, namely, vibrations of the air filled therein. Further, as thedamper is adhered to the inside of the tread portion, vibrations of thetread portion can be reduced.

During running, the tread portion is deformed such that the part in theground contacting patch becomes relatively flat whereas the remainingmajor part is generally cylindrical. Accordingly, the boundary betweenthe flat part and the cylindrical part has a relatively small radius ofcurvature. The boundary having such small-radius-curvature movesrelatively around the tire axis as the tire rotates. Accordingly, adamper fixed to the inner surface of the tread portion is repeatedlysubjected to bending deformation and compressive and tensile strain.

Therefore, the noise damper potentially tends to separate partially fromthe tire during long-term use or under high-temperature or very coldservice conditions.

on the other hand, double-sided adhesive tapes are now widely used invarious fields as being a simple and easy way of fixation. But, along-term use within a pneumatic tire is, for the double-sided adhesivetapes, yet an unknown category of usage, and a method for evaluating thedouble-sided adhesive tapes suitable for tires is not yet established.

SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide a methodfor manufacturing a pneumatic tire having a noise damper, in which thenoise damper can be stably and tightly fixed to the inner surface of thetread portion by the use of a double-sided adhesive tape selectedaccording to new criteria.

According to the present invention, a method for manufacturing apneumatic having a noise damper comprises the steps of: preparing avulcanized tire; buffing the inner surface of the tread portion of thetire; and fixing a noise damper to the buffed inner surface by the useof an double-sided adhesive tape, wherein

-   the noise damper is made of a sponge material having a specific    gravity of 0.005 to 0.060, and-   the double-sided adhesive tape has an adhesive force in a range of    not less than 1.8 Newton/20 mm tape width when measured according to    a T-shape separation test at 25 degrees C.

As a result of researches and studies made by the inventor, new criteriafor the double-sided adhesive tape was established. According thereto,the double-sided adhesive tape has to possess at least an adhesive forcewithin the above-mentioned range, and it is desirable that the followingconditions are satisfied furthermore:

-   (1) the double-sided adhesive tape has a cold-resistant property    such that, when the tape undergoes a 90-degree slide bending test at    −35 degrees C., the double-sided adhesive tape is not broken and    does not separate from the objects, namely the noise damper and tire    rubber;-   (2) the double-sided adhesive tape has a heat-resistant property    such that when the tape undergoes a T-shape separation test at 120    degrees C., the double-sided adhesive tape is not broken and does    not separate from the objects, and as a result, a cohesion failure    is caused in the noise damper; and-   (3) the double-sided adhesive tape has a water-resistant property    such that when the tape undergoes a T-shape wet separation test, the    double-sided adhesive tape is not broken and does not separate from    the objects, and as a result, a cohesion failure is caused in the    noise damper.

Further, it was also found as being preferable that:

-   (4) the double-sided adhesive tape has a tensile strength of at    least 10 Newton/10 mm-width;-   (5) the double-sided adhesive tape has a thickness of at most 0.38    mm; and-   (6) the double-sided adhesive tape has two layers of different    pressure sensitive adhesives, one suitable for the tire rubber, and    the other suitable for the noise damper.    ** Definitions    * T-Shape Separation Test

In this specification, T-shape separation test is defined as follows.

First, a test specimen TP is made as shown in FIG. 7, wherein a spongestrip 4S materially same as the noise damper is adhered to one side 5 aof the double-sided adhesive tape 5, and a rubber strip 9S materiallysame as the inner surface layer of the tire is adhered onto the otherside 5 b.

The surface of the rubber strip 9S has a smooth surface whose ten-pointaverage roughness RZ (Japanese Industrial Standard B0601) is at most 10(micrometer), and the surface is cleaned up with a detergent and driedout before adhered.

In order that the sheets 4S and 9S wholly adhere to the adhesive tape, arubber roller is reciprocated two times on each sheet at a speed of 300mm/minutes with a load of 10 kg, and then the test specimen TP is aged72 hours at room temperature.

The size of the sponge strip 4S is 10 mm in thickness, 20 mm in widthand 120 mm in length. The size of the rubber strip 9S is 1 mm inthickness, 20 mm in width and 120 mm in length. The width of thedouble-sided adhesive tape 5 is 20 mm, and the length is 80 mm. Anon-adhered part M of 20 mm length is formed in each end portion of thetest specimen TP.

The test specimen TP is attached to a tensile testing machine in a formof “T” as shown in FIG. 8, and the sheets 4S and 9S in one of thenon-adhered parts M are pulled towards opposite directions at a speed of300 mm/minute.

The tension (N) when either the sheet 4S or 9S start to separate fromthe double-sided adhesive tape 5 is measured.

* T-Shape Separation Test at 25 Degrees C.

This test means literally the T-shape separation test be carried out atabout 25 degrees C. To be precise, the T-shape separation test iscarried out, using the test specimen having a normal temperature of 25degrees C. with a tolerance of plus/minus 2 degrees C.

* T-Shape Separation Test at 120 Degrees C.

This test means that the T-shape separation test is carried out, usingthe heated test specimen. To be specific, the test specimen is put in anoven of 120 degrees C. with a tolerance of plus/minus 2 degrees C. so asto be heated to the temperature. Then, the test specimen is took outtherefrom, and the T-shape separation test is carried out at normal roomtemperature, using the hot test specimen within 2 minutes after tookout.

*T-Shape Wet Separation Test Means

This test means that the T-shape separation test is carried out, usingthe wet test specimen. The test specimen TP is soaked in water for 72hours. Then, the test specimen is took out, and the T-shape separationtest be carried out, using the wet test specimen within 2 minutes aftertook out.

* 90-Degree Slide Bending Test

90-degree slide bending test is defined in this specification asfollows. In this test, a test specimen TP as described above and a testtable M are used. As shown in FIG. 9, the test table M has two smoothflat faces (a horizontal face P1 and a vertical face P2) which areperpendicular to each other, and a corner CP therebetween is rounded bya radius R of 1 mm. The test specimen TP is first placed on one of thetwo faces so that the rubber strip 9S contacts with the flat face.

Only the both ends of the rubber strip 9S are gripped with chuck, clampor the like. Then, the test specimen TP is slid on the above-mentionedone of the flat faces to the other through the corner CP, keeping thecontact of the rubber strip 9S with the faces. The speed TP to passthrough the corner CP is 2 cm/sec. After the adhesive tape 5 completelypasses through the corner CP, the test specimen TP is visually checkedwhether the adhesive tape 5 is separated or not, whether the spongestrip 4S is broken or not.

* 90-degree Slide Bending Test at −35 Degrees C.

This test means the 90-degree slide bending test be carried out usingthe frozen test specimen.

To be specific, the test specimen is put in a freezing chamber at −35degrees C. with a tolerance of plus/minus 2 degrees C. for one hour.Then, the test specimen is took out therefrom, and the 90-degree slidebending test is carried out at normal room temperature using the coldtest specimen within 2 minutes after took out.

* Specific Gravity

The specific gravity of the sponge material is determined based on theapparent density measured according to the Japanese Industrial StandardK6400 “Soft urethane foam test method”. Para. 5 “Apparent density”.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in detail inconjunction with the accompanying drawings.

FIG. 1 is a cross sectional view of an assembly of a wheel rim and apneumatic tire with a noise damper according to the present invention.

FIG. 2 is a schematic cross sectional view of the assembly taken along aline A-A of FIG. 1.

FIG. 3 is a schematic cross sectional view of the tire for explaining amethod for buffing the inner surface of the tread portion.

FIG. 4 is an enlarged cross sectional view of the buffed surface.

FIG. 5 is a cross sectional view of the pneumatic tire to which thenoise damper is adhered.

FIG. 6 is a cross sectional view of another example of the noise damper.

FIG. 7 is an exploded perspective view of a test specimen used forevaluating adhesive properties of the double-sided adhesive tape.

FIG. 8 is a diagram for explaining the T-shape separation test.

FIGS. 9 a, 9 b and 9 c are diagrams for explaining the 90-degree slidebending test.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

According to the present invention, a pneumatic tire 3 has a troidalhollow body comprising a tread portion 3 t, a pair of axially spacedbead portions 3 b and a pair of sidewall portions 3 s extending betweenthe tread edges and the bead portions 3 b, and the tire is provided inthe hollow with a noise damper 4. As usual, the hollow body includes thefollowing reinforcing structures: a bead core 11 disposed in each of thebead portions 3 b; a carcass 6 extending between the bead portions 3 bthrough the tread portion 3 t and sidewall portions 3 s; and a belt 10disposed radially outside the carcass 6 in the tread portion 3 t.

The inner surface layer of the tire is made of an air-impermeable rubbercompound. Usually, an innerliner 9 separate from the carcass 6 isdisposed to cover the inner surface 3 i of the tire. But, it may bepossible to use the carcass topping rubber as an airtight rubber layerinstead of using the separate innerliner.

In this embodiment, the pneumatic tire 3 is a radial-ply tire forpassenger cars, and the noise damper 4 is adhered to the inner surface 3ti of the tread portion 3 t.

The tire 3 is mounted on a wheel rim 2 and the tire hollow forms aclosed cavity (i) to be filled with air. The noise damper 4 is confinedwithin the tire cavity.

The wheel rim 2 comprises: a pair of bead seats for tire beads; a pairof flanges extending radially outwardly from the bead seats; and a rimwell between the bead seats for tire mounting operation. In thisexample, the wheel rim is fixed to a centersection (spoke or disk) 2 battached to the vehicle's axle to form a two-piece wheel. Of course therim may be a part of a one-piece wheel. The wheel rim may be aspecially-designed rim, but in this embodiment, a standard wheel rim isused.

Here, the standard wheel rim is a wheel rim officially approved for thetire by standard organization, i.e. JATMA (Japan and Asia), T&RA (NorthAmerica), ETRTO (Europe), STRO (Scandinavia) and the like. Theundermentioned standard pressure and the standard tire load are themaximum air pressure and the maximum tire load for the tire specified bythe same organization in the Air-pressure/Maximum-load Table or similarlist. For example, the standard wheel rim is the “standard rim”specified in JATMA, the “Measuring Rim” in ETRTO, the “Design Rim” inTRA or the like. The standard pressure is the “maximum air pressure” inJATMA, the “Inflation Pressure” in ETRTO, the maximum pressure given inthe “Tire Load Limits at various Cold Inflation Pressures” table in TRAor the like. The standard load is the “maximum load capacity” in JATMA,the “Load Capacity” in ETRTO, the maximum value given in theabove-mentioned table in TRA or the like. In case of passenger cartires, however, the standard pressure and standard tire load areuniformly defined by 200 kPa and 88% of the maximum tire load,respectively.

The above-mentioned carcass 6 is composed of at least one ply 6A ofcords arranged radially at an angle in the range of from 70 to 90degrees with respect to the tire equator C, extending between the beadportions through the tread portion and sidewall portions, and turned uparound the bead core 11 in each bead portion from the axially inside tothe axially outside of the tire to form a pair of turnup portions 6 band a main portion 6 a therebetween. In this embodiment, the carcass 6is composed of a single ply 6A of organic fiber cords arranged radiallyat an angle of 90 degrees with respect to the tire equator C.

Between each of the turned up portions 6 b and the main portion 6 a, abead apex 8 made of a hard rubber compound is disposed to reinforce thebead portion and sidewall lower portion. The bead apex 8 extendsradially outwardly from the bead core while tapering to its radiallyouter end.

The belt comprises a breaker 10 and optionally a band. In thisembodiment, the belt consists of a breaker 10.

The breaker 10 comprises at least two cross plies: a radially inner ply10A and a radially outer ply 10B, each made of steel cords laid at anangle of about 10 degrees to about 35 degrees with respect to the tireequator C. Each of the two cross plies extends across almost entirewidth of the tread portion 3 t.

The band is usually disposed on the radially outside of the breaker 10to improve the high-speed durability of the tread portion. The band hasa so called jointless structure formed by spirally winding at least onecord at an angle of not more than 5 degrees with respect to the tireequator.

The innerliner 9 is disposed on the inside of the carcass 6 to coversubstantially entire inner surface of the tire. The innerliner 9 is madeof an air-impermeable rubber compound which contains at least 60 partsby weight of butyl rubber with respect to 100 parts by weight of all therubber component. Preferably, the butyl rubber content is at least 70parts by weight, more preferably at least 80 parts by weight, and at themaximum, 100 parts by weight. Further, halogenated butyl rubber can beincluded as the butyl rubber.

In the case that the butyl rubber content is less than 100 parts byweight, as the rest of the rubber component, diene rubber, e.g. naturalrubber, butadiene rubber, styrene-butadiene rubber, isoprene rubber,chloroprene rubber, acrylonitrile butadiene rubber and the like can beincluded.

As usual, the air-impermeable rubber compound may further containvarious additives, for example, vulcanizing agent, vulcanizationaccelerator, antidegradant, reinforcing filler, and the like.

In this example, the innerliner rubber comprises 70 PHR of butyl rubber,30 PHR of natural rubber, 60 PHR of carbon black and additives.

In order to further increase the adhesion between the innerliner 9 andthe carcass topping rubber, an intermediate layer 12 can be disposedtherebetween as shown in FIG. 4, wherein, to be superior in adhesion toboth of the carcass topping rubber and the innerliner rubber, theintermediate layer 12 is made of a rubber compound containing at least70 parts by weight of diene rubber (especially preferably naturalrubber) with respect to 100 parts by weight of the rubber component, andthe layer 12 has a thickness of at most 1.0 mm.

* Noise Damper

The noise damper 4 is fixed to the inside of the tread portion.Accordingly, to deform easily during running and not to affect therunning performance such as steering stability, the material of thedamper must be a light-weight low-density flexible material, e.g. formedrubber, foamed synthetic resins, cellular plastics and the like. In thecase of foamed materials (or sponge materials), an open-cell type and aclosed-cell type can be used, but an open-cell type is preferred. Forexample, synthetic resin sponges such as ether based polyurethanesponge, ester based polyurethane sponge, polyethylene sponge and thelike; rubber sponges such as chloroprene rubber sponge (CR sponge),ethylene-propylene rubber sponge (EDPM sponge), nitrile rubber sponge(NBR sponge) and the like can be used.

Especially, polyethylene sponge, polyurethane sponges including etherbased polyurethane sponge and the like are preferably used in view ofnoise damping effect, lightness in weight, easy control of expansionrate and durability.

In this embodiment, an open-cell type sponge material, morespecifically, polyurethane foam is used.

Depending on the environment where the tire is used, there is apossibility that the air which fills the tire cavity (i) to inflate thetire is humid and the water makes condensation in the closed cavity (i).Accordingly, sponge materials which are hard to be hydrolyzed such asether based polyurethane are suitably used.

Further, in order to prevent water from penetrating into the noisedamper, a water repellent treatment can be preferably made on the spongematerial. Also, a mildewproof treatment can be preferably made.

Furthermore, in order to avoid poison in the emission gas generated whenincinerating scrap tires, it is preferred that raw materials notincluding halogen are used to make the sponge material.

By disposing a certain volume of the sponge material in the tire cavity(i), resonances of the air in the cavity can be controlled andvibrations of the tread portion is reduced. Therefore, noise generatedfrom the tire during running can be reduced.

If the specific gravity of the sponge material is less than 0.005 ormore than 0.06, it becomes difficult to control the cavity resonance.Therefore, the specific gravity is not less than 0.005, preferably notless than 0.010, more preferably not less than 0.016, but not more than0.060, preferably not more than 0.05, more preferably not more than0.045.

If the volume V2 of the noise damper 4 is less than 0.4% of the volumeV1 of the tire cavity, it is difficult to reduce the noise sound levelrecognizably. If the volume V2 is more than 20% of the volume V1, itbecomes difficult to maintain the tire weight balance. Therefore, thevolume V2 of the sponge material of the noise damper 4 is at least 0.4%,preferably not less than 1.0%, more preferably not less than 2.0%, stillmore preferably not less than 4.0%, but not more than 20%, preferablynot more than 10% of the volume V1 of the tire cavity.

In the case that two or more noise dampers 4 are disposed in the tirecavity, the above-mentioned volume V2 means the total volume of all thenoise dampers in the tire.

The volume V1 of the tire cavity 4 is measured under thenormally-inflated unloaded state of the tire. Here, thenormally-inflated unloaded state of the tire is such that the tire ismounted on the wheel rim and inflated to the standard pressure butloaded with no tire load.

Incidentally, the volume V1 of the cavity (i) can be obtained by thefollowing approximate expression (1):V=A×{(Di−Dr)/2+Dr}×piwherein

-   “A” is the cross sectional area of the cavity (which can be obtained    by computed tomography scan for example),-   “Di” is the maximum diameter of the cavity,-   “Dr” is the wheel rim diameter, and-   “pi” is the circle ratio.    These parameters are measured under the normally-inflated unloaded    state of the tire.

In view of the radial force variation, radial run out and the like, itis preferable that the noise damper 4 has a substantially constant crosssectional shape along the entire circumferential length thereof exceptfor the end portions 4 e of the damper 4. In the case that the ends ofthe damper are not connected to each other, it is preferable that theend portions 4 e are tapered as shown in FIG. 2 to prevent frictiontherebetween.

Further, in order to prevent leaning of the damper 4 during high speedrunning, the height SH of the noise damper 4 is preferably not more than50 mm, more preferably not more than 30 mm, still more preferably notmore than 25 mm, but not less than 10 mm, more preferably not less than15 mm. Here, the height SH is measured perpendicularly to and from thetire inner surface 3 ti to the extreme end of the noise damper 4 underthe condition that the tire is not yet mounted on the rim.

As to the cross sectional shape of the noise damper, a symmetrical shapeis preferred because, if the cross sectional shape is asymmetrical, dueto the difference in the lateral stiffness (rigidity) between theright-hand side and the left-hand side of the damper, the damper isliable to lean during running, especially during high-speed running, andthe balance of the tire alters.

In the case of a single noise damper 4 having a symmetricalcross-sectional shape, it is preferable that its center is aligned withthe tire equator C, whereby an eccentric load on the noise damper 4 isminimized to prevent the damper from leaning.

The cross sectional shape in this example is a rectangle (width W0=70mm, height SH=30 mm), but various shapes, e.g. trapezoid, triangle,semicircle, parabolic/bullet shape etc., can be used. Further, asymmetrical shape having two humps as shown in FIG. 6 can be used.

* Double-Sided Adhesive Tape

The noise damper 4 is fixed to an inner surface of the tread portion,using a double-sided adhesive tape 5.

As to the double-sided adhesive tape 5,

-   (1) a tape having a base tape 5S with a coat 5P or layer of an    adhesive material on one side 5 a and a coat 5P or layer of an    adhesive material on the other side 5 b as shown in FIG. 7,-   (2) a tape having no base tape and made up of only double layers 5P    of different adhesive materials, and-   (3) a tape made up of only a single layer 5P of an adhesive material    can be used.

The base tape 5S is, for example: plastic film such as polyester; sheetof plastic foam such as acrylic foam; nonwoven fabric or bondedmaterial; a woven textile; and the like.

As to the adhesive material, for example, a rubber-based adhesivecomprising natural rubber and/or synthetic rubber and additives, e.g.tackifier, softener, age resistor and the like; an acrylic pressuresensitive adhesive comprising a plurality of copolymers of an acrylicester and a polyfunctional monomer having different glass-transitiontemperatures (containing pressure sensitive adhesives of high heatresistant type, flame resistant type and low-temperature adhesion type);a silicone pressure sensitive adhesive comprising a silicone rubber anda resin; a polyether adhesive; a polyurethane adhesive and the like canbe suitably used.

The use of a thermosetting adhesive comprising a thermosetting resin,e.g. epoxy resin or the like is not preferred in view of the productionefficiency because the adhesive needs to be heated up to about 130degrees C. for about 30 minutes.

As to the adhesive materials, it is possible to use the same adhesivematerial, but, it is desirable to use different types of adhesivematerials in the above case (1) or (2). For example, a rubber adhesivewhich adheres strongly to the tire rubber, and an acrylic pressuresensitive adhesive which adheres strongly to the noise damper are usedon the respective sides.

In order to prevent the noise damper 4 from separating from the tireinner surface 3 ti even under severe service conditions, a quantitativestudy was made on the adhesive force. As a result, it was discoveredthat separation failures occurring under normal running conditions ispreventable if the adhesive force shows a value not less than 1.8Newton/20 mm-width when measured according to the T-shape separationtest, using a test specimen TP which is as shown in FIG. 7, made up of adouble-sided adhesive tape 5, a strip 4S of the sponge material appliedto one side of the tape, and a strip 9S of the innerliner rubber appliedto the other side of the tape.

It is however, preferable that the adhesive force is at most 7.0Newton/20 mm-width in order that the tape can be removed together withthe noise damper if the damper is broken for any reason.

It is especially preferable that the strip 4S of the sponge material isbroken prior to separating from the tape 5 when the T-shape separationtest at 25 degrees C. is carried out. Namely, the adhesive force at 25degrees C. is not less than 2.7 Newton/20 mm-width, preferably not lessthan 3.3 Newton/20 mm-width.

On the other hand, for preventing the adhesive tape 5 from being crackeddue to hardening under low temperature conditions, it is desirable thatcracks visible to the naked eye and separation do not occur when the90-degree slide bending test at −35 degrees C. is carried out.

Further, for preventing the adhesive force from decreasing due tosoftening of the adhesive material under high temperature conditions, itis desirable that the strip 4S of the sponge material is broken prior toseparating from the tape 5 when the T-shape separation test at 120degrees C. is carried out.

Furthermore, for preventing the adhesive force from decreasing due towater penetrating into the noise damper 4, it is desirable that thestrip 4S of the sponge material is broken prior to separating from thetape 5 when the T-shape wet separation test is carried out.

The durability of the double-sided adhesive tape 5 has a tendency todecrease as the thickness increases. The tread portion is subjected to arelatively large bending deformation at the circumferential ends of theground contacting patch. Accordingly when the tape is thick, the sharingstress between the tape and the tire inner surface becomes large, and acohesion failure of the adhesive material layer tends to occur.Therefore, it is preferable that the thickness of the double-sidedadhesive tape 5 is not more than 0.38 mm.

For the base tape 5S of such thin tape, a flexible material such asacrylic foam is preferably used.

In order to replace the damaged noise damper, or to recycle the usedtire for example, it is desirable that the noise damper 4 can be easilyremoved from the tire together with the tape. Accordingly, thedouble-sided adhesive tape 5 is required to have a certain degree ofbreaking strength.

Therefore, the breaking strength of the double-sided adhesive tape 5 ispreferably at least 10 Newton/10 mm-width, more preferably not less than15 Newton/10 mm-width.

The breaking strength is measured according to Japanese IndustrialStandards Z0237 “Testing methods of pressure-sensitive adhesive tapesand sheets”.

Incidentally, in case of the adhesive tape having no base tape, it isdifficult to remove the tape namely the adhesive material layer(s).Thus, in this view, the use of such tape is not preferable.

* Manufacturing Method

The pneumatic tire can be manufactured as usual. Namely, raw tirecomponents, e.g. tread rubber, sidewall rubber, bead rubber, bead apexrubber, innerliner rubber, carcass ply, belt plies and the like areassembled into a raw tire, using a tire building drum. The raw tire isput in a vulcanizing mold, and an inflatable bladder is inserted in thetire hollow. On these occasions, a mold lubricant or release agent isapplied between the tire and the mold and also between the tire and thebladder. Then, the bladder is inflated, and the tire is heated tovulcanize the tire. After the tire has been vulcanized, the tire isremoved from the mold.

As well known in the tire art, the bladders are conventionally providedon the outer surface with vent grooves to remove air between the tireinner surface and bladder. In this embodiment, however, a specialbladder whose outer surface has a smooth part devoid of vent grooves anda part provided with vent grooves is used. The position of the smoothpart corresponds to the position to which the damper is fixed.

In the next place, in order to remove the mold release agent, an area Yof the tire inner surface to which the noise damper is adhered isbuffed. Namely, the surface of the innerliner 9 of the vulcanized tireis buffed annularly along the tire equator. The above-mentioned smoothpart of the bladder correspond to the area Y, therefore this area Y isdevoid of the ribs resulting from the vent grooves.

To remove the mold release agent completely, the thickness (h) of thesurface layer buffed off needs at least 3.0%, preferably 5.0% or more ofthe original thickness (t) of the innerliner 9. If however, thethickness (h) of the surface layer buffed off is too much, there is apossibility that the airtightness and durability of the innerliner aredeteriorated. Therefore, the thickness (h) should be not more than 30%of the original thickness (t), preferably not more than 10.0% in view ofthe working efficiency and tire production cost.

If it is necessitated to compensate for a possible deterioration of theairtightness owing to the reduced thickness, it is preferred that thebutyl rubber content of the innerliner is increased to over 70 parts byweight, more preferably over 80 parts by weight.

Incidentally, in the case of finished tires (if it is difficult to knowthe original thickness), the thickness (h) of the buffed-off surfacelayer is determined as the difference t1−t2, wherein

-   -   t2 is the thickness of the buffed innerliner 9 which is defined        by the average of values measured at four circumferentially        different measuring positions set at each of three axial        positions P: a position Pc at the tire equator C; and a position        Pe 10 mm axially inward of each of the axial edges Ye of the        buffed area Y, namely, the average of values measured at twelve        measuring positions, and    -   t1 is the original thickness of the innerliner 9 which is        defined by the average of values measured at four        circumferentially different measuring positions set at each of        two axial positions Q each being 10 mm axially outward of each        of the axial edges Ye of the buffed area Y, namely, the average        of values measured at eight measuring positions.

The axial width W1 of the buffed area Y is more than the width W0 of thestrip of the sponge material, and preferably the difference W1-W0 is atleast 5.0 mm.

The buffed area Y is formed within the maximum axial width WB of thebelt 7, and preferably the axial distance from each of the axial edgesof the belt 10 to the adjacent edge of the buffed area Y is more than10.0 mm.

In the cross section of the tire, the bending deformation of the tireduring running is relatively small under the belt, and the bendingdeformation becomes increased near the belt edges. Therefore, in orderto prevent damages such as cracks in the thickness-reduced area Y of theinnerliner 9, it is desirable to provide the axial distance of more than10.0 mm.

The vulcanized tire removed from the mold is, as shown in FIG. 3, helduprightly and rotatably around its rotational axis by straddling betweena pair of horizontal parallel driving rollers 21. To hold the tireuprightly, guide rollers 22 are disposed on each side of the tire. Whenthe power is applied to the driving rollers 21, the two rollers 21rotate in the same direction, and accordingly the tire is rotated in thereverse direction.

Next, a buffing disk 20 is inserted in the tire hollow through thecenter hole 2H of the tire.

The tire 1 is rotated by turning on the driving rollers 21, and thebuffing disk 20 is moved downward slowly.

At that time, the buffing disk 20 is kept to be freely rotatable byturning off the driving motor 20M of the buffing disk 20. Accordingly,when the outer peripheral surface of the buffing disk 20 comes intocontact with the inner surface of the tread portion of the rotatingtire, the buffing disk 20 starts to rotate.

By the use of a sensor 20D for detecting the rotation of the buffingdisk 20, when the start of the rotation is detected during moving downof the buffing disk 20, the driving motor 20M of the buffing disk 20 isturned on, and the moving down is stopped after the buffing disk 20 ismoved downward by a predetermined distance from the position or heightat which the buffing disk 20 starts to rotate. As a result, the buffingdisk is rotated in the reverse direction to the rotational direction ofthe tire, and the tire is buffed.

In order to buff evenly, suitably used as the buffing disk 20 is abuffing brush in which metal or synthetic resin bristles 20B areradially fastened into a cylindrical core 20C. Preferably, bristles madeof a synthetic resin containing abrasive grains of alumina or siliconcarbide are used.

In the case of the buffing brush, clogging is hard to occur, and thebristles are easily curved and moved along the profiled inner surface ofthe tread portion. As a result, the surface can be evenly buffed off bya small thickness.

The reason for turning on the driving motor 20M of the buffing disk 20after the buffing disk 20 starts to rotate following the rotated tire,is as follows:

-   With respect to the position of the inner surface of the tread    portion or the inside diameter of the tread portion, the tires have    relatively large variations when compared with the thickness of the    surface layer to be buffed off.-   Further, the outside diameter of the buffing disk 20 also varies in    use because of the wear and deformation of the bristles. Therefore,    it is important in precisely buffing off the surface layer to    determine the reference position, at which the outer peripheral    surface of the buffing disk 20 contacts with the inner surface of    the tread portion, every time a tire is changed. And, the moving    down distance of the buffing disk 20 has to start from this    reference position.

In this example, the buffing disk 20 has a width W2 equal to the widthW1 of the buffed area Y is used to remove the necessity for moving thebuffing disk 20 in the tire axial direction during buffing. Of course,by moving the buffing disk 20 in the tire axial direction, the buffingdisk 20 having a narrower width than the buffed area Y can be used.

After the tire makes the predetermined number of turns, the buffing disk20 is moved up to be detached from the inner surface of the tire, andthe driving motor is turned off. The driving rollers 21 are alsostopped. The buffing disk 20 is removed from the tire hollow.

Thus, the tire provided in the inner surface of the tread portion withthe buffed area Y is produced.

Next, the double-sided adhesive tape 5 satisfying at least one of theabove-mentioned conditions (1)-(6) is selected. And the noise damper isfixed to the buffed area Y by the use of the double-sided adhesive tape5.

Firstly, the double-sided adhesive tape 5 is applied to the noise damperor a strip of the sponge material, and then by removing the releasedpaper from the other side of the tape, the damper is applied to thebuffed area Y.

Thus, the tire with the noise damper is produced.

* Comparison Tests

Radial tire of size 215/45R17 (Rim size 17×7JJ) for passenger cars wereprepared, and tested for the durability and airtightness of the tire andthe adhesion of the damper.

When vulcanizing the tires, an aqueous solution containing silicone andmica powder was used as the mold release agent, and such mold releaseagent remained on the inner surface of the tire. Therefore, the surfaceof the innerliner in the tread portion was buffed as shown in Table 1.The noise damper was fixed to the buffed face, using a double-sidedadhesive tape.

As the buffing disk, a buffing brush having a diameter of 300 mm wasused. The buffing brush had 0.9 mm dia. bristles made of nyloncontaining silicon carbide grit (TORAYGRIT manufactured by TORAYMONOFILAMENT CO., LTD.: Abrasive grain size 240).

As the noise damper, a strip of ether based polyurethane sponge (INOACCORPORATION, Product No. ESH2) having a specific gravity of 0.039 wasused. The damper had a rectangular cross sectional shape, and the sizethereof was 20 mm in height and 97 mm in width.

As the double-sided adhesive tape, a heat-stable tape having a nonwovenbase tape and acrylic pressure sensitive adhesive (Ebisu chemical co.,Ltd., #700) was used.

1) Durability and Adhesivity Test

Using a tire test drum, the tire mounted on a standard rim was run for12,000 km at a speed of 80 km/h, under the following conditions:

-   -   Inner pressure of 230 kPa    -   Tire load of 6.2 kN (120% of the tire load limit for 230 kPa        specified by JATMA)        After running, the innerliner was checked for damage, and the        damper was visually checked whether it adhered thoroughly or        not. The results are indicated in Table 1, wherein OK indicates        that there was no problem,

-   1 indicates that the innerliner was cracked, so the carcass cords    were exposed,

-   2 indicates that the small cracks were caused on the surface of the    innerliner,

-   3 indicates that the adhesive tape did not adhere to the inner    surface,

-   4 indicates that the adhesive tape adhered to the inner surface at    first, but separated after running.    2) Airtightness Test

The tires mounted on the standard rim and inflated to 230 kPa were putin a hot chamber at 80 degrees C. for 15 days and then the retainedpressure was measured. The results are indicated in Table 1, using anindex based on Control tire being 100, wherein the larger the indexvalue, the better the airtightness.

TABLE 1 Tire Control Ref. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7Ex. 8 Ex. 9 Innerliner Butyl rubber content (wt %) 60 60 60 60 60 60 6060 60 70 80 Original thickness t (mm) 1.25 1.28 1.25 1.22 1.23 1.2 1.231.16 1.3 1.32 1.35 Thickness h of Buffed-off 0 0.52 0.11 0.25 0.36 0.040.01 0.13 0.12 0.25 0.26 surface layer (mm) h/t (%) 0 40 9 20 29 3 0.811 9 19 19 Width W1 of Buffed area — 110 110 110 110 110 110 178 190 110110 Y (mm) Belt width WB (mm) 178 178 178 178 178 178 178 178 178 178178 Noise damper width W0 (mm) 97  97 97 97 97 97 97 97 97 97 97 Testresults Durability OK *1 OK OK OK OK OK OK *2 OK OK Adhesivity *3 OK OKOK OK OK *4 OK OK OK OK Airtightness 100 70 98 95 92 99 100 — — 102 106

1. A pneumatic tire comprising a tread portion having an inner surfaceand an outer surface defining a ground contacting face, a pair ofsidewall portions, a pair of bead portions, a carcass extending betweenthe bead portions through the tread portion and sidewall portions, abelt disposed radially outside the carcass in the tread portion, and anoise damper, wherein the tread portion includes an innerliner of anair-impermeable rubber compound defining said inner surface, the innersurface is provided with a buffed area, where the thickness (h) of thebuffed-off surface of the innerliner is not less than 3% but not morethan 30% of the thickness (t) of the innerliner, and the axial distancefrom each of the axial edges of said belt to the adjacent edge of saidbuffed area is more than 10.0 mm, and said noise damper is fixed to thebuffed area by the use of a double-sided adhesive tape.
 2. A method forfixing a noise damper to an inner surface of a tread portion of apneumatic tire, the tire comprising a tread portion having an innersurface and an outer surface defining a ground contacting face, a pairof sidewall portions, a pair of bead portions, a carcass extendingbetween the bead portions through the tread portion and sidewallportions, and a belt disposed radially outside the carcass in the treadportion, the method comprising the steps of: buffing the inner surfaceof the tread portion; and using a double-sided adhesive tape to fix thenoise damper to the buffed inner surface, wherein the tread portionincludes an innerliner of an air-impermeable rubber compound definingsaid inner surface, and in the step of buffing the inner surface of thetread portion, the thickness of the buffed-off surface layer of theinnerliner is controlled not to exceed 30% of the thickness of theinnerliner, and the axial distance from each of the axial edges of saidbelt to the adjacent edge of said buffed area is more than 10.0 mm. 3.The method according to claim 2, wherein in the step of buffing theinner surface of the tread portion, the thickness of the buffed-offsurface of the innerliner is controlled not to fall below 3% of thethickness of the innerliner.